1. Field of the Invention
This invention relates to a method of manufacturing recess/projection structures with very fine intervals of a scale of nanometers. This invention also relates to a magnetic device using a structure.
2. Related Background Art
So-called nano-imprinting methods have been proposed in recent years as techniques for forming micro-structures of dimensions of nanometers on the surface of an object to be processed by directly pressing a mold of recess/projection structures against the object (see, inter alia, U.S. Pat. No. 5,772,905 and Japanese Patent Application Laid-Open No. 2000-232095). They represent new technological developments and do not relate to lithography that uses light and/or an electron beam.
With any of the proposed techniques, a mold 101 prepared through a process using an electron beam as shown in FIGS. 6A, 6B, 6C, 6D and 6E of the accompanying drawings and having a pattern of projection structures that are arranged at intervals of tens to hundreds of several nanometers is pressed against the resist 102 formed on a flat semiconductor wafer 103 and then removed to produce a pattern of recess/projection structures. Then, the recess structures 104 are removed by ion-milling and the product of ion-milling is used as mask for etching the semiconductor wafer 103 to produce structures of a size of nanometers including recesses/projections that corresponds to the original stamper. With the technique, it is possible to form a micro-pattern easily within a short period of time that cannot be realized by photolithography. Additionally, the substrate and the mold are prevented from being destroyed as the pressure of the press operation is reduced by means of a resin layer and etching is used for the actual processing operation.
Meanwhile, there are also known techniques for forming an alumina nano-hole at any selected position by preparing a recess structure on the surface of an aluminum thin film, using photolithography, direct writing with a beam or a press technique as described above, and conducting an anodization (anodic oxidation) process, using the recess as starting point for forming the nano-hole (see, inter alia, Japanese Patent Application Laid-Open No. H10-121292). However, recesses/projections formed on the surface of a metal thin film by agglomerations of grains have a height of several to tens of several nanometers, they can be obstacles when forming a very fine starting point pan em (to be referred to as nano-structures hereinafter) on the surface of the thin film that shows gaps substantially as large as the above cited height.
A metal thin film of the type under consideration is formed not completely by single crystals but by a number of agglomerations of crystal grains. Steps are produced at the crystal boundaries. In other words, recesses/projections are formed on the surface of the thin film.
FIGS. 7A, 7B, 7C, 7D, 7E and 7F illustrate a technique for avoiding such recesses/projections. Referring to FIGS. 7A, 7B, 7C, 7D, 7E and 7F, an electro-conductive layer 202, an insulation layer 201 and a resist layer 204 are sequentially formed on a support substrate 203 (FIGS. 7A and 7B) and then a pattern of recesses 205 is formed in the resist layer 204 by photolithography or an interference exposure technique (FIG. 7C). Then, the electro-conductive layer 202 is made to become exposed by etching the insulation layer, using the resist pattern as mask (FIG. 7D). Then, an aluminum film 206 is arranged thereon and subjected to anodization. With the above-described process, nano-holes can be formed as a pattern on the electro-conductive layer due to the electric current that flows from the exposed parts of the electro-conductive layer 202 (FIGS. 7E and 7F). While recess structures may be formed as a pattern on the aluminum film as shown in FIG. 7E, it accelerates the formation of nano-holes aligned with the pattern of the electro-conductive layer and hence does not give rise to any problem. Thus, it is possible to prepare nano-holes arranged at very fine intervals without being affected by the recesses/projections of agglomerations of grains on the surface of the aluminum film.
Techniques for filling such regular nano-structures with metal, semiconductor or a magnetic material have also been proposed along applications of the techniques including coloring, magnetic recording mediums, EL light emitting elements, electrochromic elements, optical elements, solar cells and gas sensors.